This patent application claims priority based on a Japanese patent application, H11-046729 filed on Feb. 24, 1999, the contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a code division multiple access base station and in particular to a code division multiple access base station and which can process a signal wave having a long delay time.
2. Description of the Related Art
To deal with the variation of the delay time of a received signal, the conventional code division multiple access (CDMA) base station measures the delay profile of a transmission path from a received signal. The delay profile is the response of a signal wave transmitted through different transmission paths received at a base station. Because the signal wave transmits through different paths, the waveform of the signal wave is transformed by the influence of each transmission path. The conventional CDMA base station then selects a plurality of peaks having an effective power level and synthesizes the selected peak to demodulate the received signal.
FIG. 1 shows a configuration of a CDMA base station. A CDMA base station has an antenna 10, a receiving unit 12, a RACH signal receiver 14, a DCH signal receiver 16, and a controller 26. The RACH signal receiver 14 has a delay profile measuring unit 18 and a demodulator 20. The DCH signal receiver 16 has a delay profile measuring unit 22 and a demodulator 24.
The antenna 10 receives a random access channel (PACH) signal and a data channel (DCH) signal which are spread spectrum modulated.
FIG. 2 shows how the RACH signal and the DCH signal are transmitted between the base station and the mobile station. First, the RACH signal is input to the base station from the mobile station to setup a c all. The RACH signal includes information such as the telephone number and a registration number of the user of the mobile station. Here, as an example, the RACH message of the RACH signal is 10 msec long. The RACH signal is transmitted by burst transmission where the communication is started and finished abruptly.
The ACH signal is then output from the base station to the mobile station. The ACH signal includes the information that the base station has acknowledged the mobile station. Then, the mobile station can start a call and sends the DCH signal to the base station. The DCH signal is a call signal set by the RACH signal. The DCH signal begins at an approximate predetermined time after the transmission of the ACH signal and finishes at a predetermined time after the commencement of the DCH signal transmission. Here, as an example, each DCH message of the DCH signal has a 10 msec time length.
The RACH signal and the DCH signal are complex signals having two-dimensions, namely an I-phase and a Q-phase. The receiving unit 12 converts the frequency of the RACH signal and DCH signal down to a baseband frequency from a carrier wave frequency band, and outputs to the RACH signal receiver 14 and the DCH signal receiver 16, respectively. The RACH signal receiver 14 receives the RACH signal from the receiving unit 12 to despread the RACH signal.
The DCH signal receiver 16 receives the DCH signal from the receiving unit 12 to despread the DCH signal. The delay profile measuring unit 18 detects a peak of the RACH signal from the receiving unit 12 and detects the time of receiving the peak of the RACH signal. The delay profile measuring unit 18 then outputs the detected peak receiving time of the RACH signal to the demodulator 20 through the controller 26. The demodulator 20 despreads the RACH signal received from the receiving unit 12 based on the peak receiving time of the RACH signal detected by the delay profile measuring unit 18. The demodulator 20 then outputs the despread and demodulated RACH signal.
The delay profile measuring unit 22 receives the DCH signal from the receiving unit 12 and detects a peak of the DCH signal and detects the time of receiving the peak of the DCH signal. The delay profile measuring unit 22 then outputs the detected peak receiving time of the DCH signal to the demodulator 20, through the controller 26. The demodulator 24 despreads the DCH signal received from the receiving unit 12 based on the peak receiving time of the DCH signal detected by the delay profile measuring unit 22. The demodulator 24 then outputs the despread and demodulated DCH signal.
The controller 26 sets a type of spreading code and timing of generation of the spreading code for despreading the RACH signal and the DCH signal for the delay profile measuring units 18 and 22. The controller 26 also inputs the peak receiving time of the RACH signal from the delay profile measuring unit 18 and outputs this to the demodulator 20. Furthermore, the controller 26 inputs the peak receiving time of the DCH signal and outputs this to the demodulator 24.
The delay profile measuring units 18 and 22 measures a delay profile with a long delay time, so that the base station can receive various delay signals sent from various places inside the cell region of the base station. During the transmission of the signals, the signals transmit on a different path so that each of the delay profiles has a different delay time. At the same time as measuring the delay profile, the controller 26 notifies the demodulators 20 and 24 of the peak receiving time of the RACH and the DCH signal, so that the demodulators 20 and 24 can despread each RACH signal and DCH signal having various delay times.
FIG. 3 shows a detailed configuration of a delay profile measuring unit 18. The delay profile measuring unit 18 can measure a delay profile having a long delay time. The delay profile measuring unit 18 has a RACH signal matched filter 28 and a RACH signal delay profile measuring unit 34. The delay profile measuring unit 18 has a plurality of RACH signal matched filters 28 to despread the RACH signals sent from the plurality of users. Only one RACH signal matched filters 28 is shown in FIG. 3 for simplicity. The RACH signal matched filter 28 has a spreading code generator 30 and a complex correlator 32. The complex correlator 32 may include complex matched filter. The RACH signal delay profile measuring unit 34 has a power level calculator 36, a delay time adjuster 38, a delay profile averaging unit 40, and a path detector 42.
The RACH signal matched filter 28 inputs a RACH signal from the receiving unit 12 and despereads the input RACH signal. The RACH signal delay profile measuring unit 34 detects the peak receiving time of the RACH signal from the despread RACH signal, and outputs the peak receiving time of the RACH signal to the controller 26.
The spreading code generator 30 generates a spreading code and outputs this to the complex correlator 32. The complex correlator 32 despreads the RACH signal using spreading code generated by the spreading code generator 30. Because the RACH signal is a complex signal having an I-phase and a Q-phase, the signal demodulated by the complex correlator 32 is also a complex signal having an I-phase and a Q-phase. The power level calculator 36 calculates the absolute value of a vector in the I-phase and the Q-phase of the demodulated RACH signal, to obtain a power level of the demodulated RACH signal. As a result of the power level calculation, the demodulated RACH signal having an I-phase and a Q-phase two-dimensional data changes to one-dimensional data.
The delay time adjuster 38 adjusts the delay times of a plurality of delay profiles having different delay times, to the same delay time. The delay profile averaging unit 40 has a memory to store the plurality of delay profiles, the delay times of which have been adjusted. The delay profile averaging unit 40 sums each of the peaks of the delay profiles as shown below in FIG. 4, so that the peak can be separated from the noise or interference components.
In this case, it is assumed that the RACH signal is spread spectrum modulated by the 256 chips of the spreading code. To enable the summing of a maximum of 5-symbol periods of the delay time, the delay profile averaging unit 40 has a memory region for 5120 words. Here, 1 chip is equal to 4 words. The 5120 words are obtained by multiplying the 256 chips by the 5 symbols and further multiplying by 4, which is an over sampling number. The path detector 42 detects the peak receiving timing of the RACH signal by detecting the peaks of the RACH signal above the threshold value.
The delay profile measuring unit 22 has the same configuration as the delay profile measuring unit 18. The difference between the delay profile measuring unit 18 and the delay profile measuring unit 22 is the spreading code used for despreading. The spreading code used for the delay profile measuring unit 18 is used for despreading the RACH signal, and the spreading code used for the delay profile measuring unit 22 is used for despreading the DCH signal. As in the delay profile measuring unit 18, the delay profile measuring unit 22 can also measure a delay profile having a long delay time such as 5 symbol periods.
FIG. 4 shows an example of a delay profile of a RACH signal output from a plurality of RACH signal matched filters 28. The delay profiles are shown relative to time. Here, the delay profile measuring unit 18 has five RACH signal matched filters 28a, 28b, 28c, 28d, and 28e in parallel, for measuring the delay profile of 5 symbol periods. One symbol period has 1024 samples. The delay profiles shown in FIG. 4 are sent from one mobile station. Because the signal wave sent from a mobile station transmits via various,paths, the base station receives delay profiles having various delay times. In FIG. 4, the output of each of the RACH signal matched filters 28a, 28b, 28c, 28d, and 28d has three peaks, one direct wave and two delayed waves. These three peaks show that the RACH signal is transmitted through three paths. The direct wave is transmitted directly from the mobile station to the base station, and the other two delay waves are transmitted by reflection.
The spreading code of the long code of the first symbol is allotted to the RACH signal matched filter 28a. The spreading code of the long code of the second symbol is allotted to the RACH signal matched filter 28b, and so on. The spreading code is comprised of a long code and a short code. The long code is used for distinguishing the specific mobile station from a plurality of mobile stations. The long code has a long period due to a plurality of symbol periods. Thus, even in the same long code, the code is different by changing the timing of generation of the code. Therefore, the long code allotted to the RACH signal matched filter 28a is different to the long code allotted to the RACH signal matched filter 28b. 
By allotting the first symbol of the long code to the RACH signal matched filter 28a for despreading, the first peaks emerge in the first symbol period. By allotting the second symbol of the long code to the RACH signal matched filter 28b for despreading, the second peaks emerge in the second symbol period, and so on. Therefore, the delay profile measuring unit 18 can measure the peaks of the RACH signal emerging during the 5 symbol periods.
The delay time adjuster 38 then delays the first peak for four symbol periods, delays the second peak for three symbol periods, delays the third peak for two symbol periods, and delays the forth peak for one symbol period. Therefore, all the peaks of the delay profiles have the same delay time for the four symbol periods. Then, each of the peaks of the five delay profiles is summed by the delay profile averaging unit 40. The peak of the direct waves of each of the delay profiles are summed. The peaks of the first delayed waves of each of the delay profiles are summed separately to the direct waves and the second delay waves. The peaks of the second delayed waves of each of the delay profiles are summed separately to the direct waves and the first delay waves. The delay profile shown below the arrow in FIG. 4 is a result of the summing of the five delay profiles.
The conventional delay profile measuring unit 22 has five signal matched filters in parallel, to measure the delay profile for five symbol periods as in the delay profile measuring unit 18. Furthermore, the delay profile averaging unit of the delay profile measuring unit 22 must have a memory region of a total of 25600 words, to store the five delay profiles for five symbol periods. Furthermore, to detect the peaks from the 5120 words, all 5120 words must be retrieved. If the path detector 42 is comprised of a digital signal processor, the path detector 42 has to process an enormous volume of data at high speed because the path detector 42 has to retrieve all 5120 words in order to detect the peaks.
Therefore, it is an object of the present invention to provide a code division multiplex receiver which overcomes the above issues in the related art. This object is achieved by combinations described in the independent claims. The dependent claims define further advantageous and exemplary combinations of the present invention.
According to the first aspect of the present invention, a base station for a mobile telephone system adopting a code division multiple access method can be provided. The base station may comprise a first delay profile measuring unit for receiving a random access channel signal, which is input to the base station for setting up a call, detecting at least one peak of the random access channel signal, and detecting a time of receiving the peak of the random access channel signal; and a data channel demodulator which despreads a data channel signal of the call set up by the random access channel signal based on the peak receiving time of the random access channel signal detected by the first delay profile measuring unit.
The base station can be provided such that the base station further comprises a second delay profile measuring unit which receives the data channel signal, detects at least one peak of the data channel signal, and detects a receiving time of the peak of the data channel signal based on the peak receiving time of the random access channel signal; and the data channel demodulator despreads the data channel signal based on the peak receiving time of the data channel signal detected by the second delay profile measuring unit.
The first delay profile measuring unit may have a first path detector which detects the peak receiving time of the random access channel signal and may output the detected peak receiving time to the second delay profile measuring unit. The second delay profile measuring unit may have a spreading code generator which generates a spreading code for despreading the data channel signal based on the peak receiving time of the random access channel signal; and the first path detector may provide to the spreading code generator the peak receiving time of the random access channel signal.
The base station may further comprises a controller which inputs the peak receiving time of the random access channel signal from the first delay profile measuring unit and outputs to the second delay profile measuring unit. The second delay profile measuring unit may have a spreading code generator which generates a spreading code for despreading the data channel signal based on the peak receiving time of the random access channel signal.
The base station can be provided such that the spreading code generator may sequentially generate a plurality of the spreading codes, each of which corresponds to the data channel signal of each of a plurality of symbol periods, based on the peak receiving time of the random access channel signal. The second delay profile measuring unit may further have: a complex correlator which despreads the data channel signal of the plurality of symbol periods using the plurality of spreading codes generated by the spreading code generator; a delay profile averaging unit which stores the despread data channel signal of the plurality of symbol periods and sums each of the stored data channel signals of the plurality of symbol periods; and a second path detector which detects the peak receiving time of the data channel signal from the summed data channel signal.
The spreading code generator may start generating the spreading code when receiving the peak of the random access channel signal. The delay profile averaging unit may start storing the despread data channel signal based on the peak receiving time of the random access channel signal. The first delay profile measuring unit may receive a plurality of the random access channel signals, detects at least one peak for each of the plurality of the random access channel signals, and detects the peak receiving time for each of the plurality of the random access channel signals.
According to the second aspect of the present invention, a method of processing a received signal for a mobile telephone system adopting a code division multiple access method can be provided. The method comprises steps of receiving a random access channel signal for setting up a call; detecting at least one peak of the random access channel signal; detecting a time of receiving the peak of the random access channel signal; and despreading a data channel signal of the call set by the random access channel signal based on the peak receiving time of the random access channel signal.
The method may further comprises steps of receiving the data channel signal; detecting at least one peak of the data channel signal; and detecting a receiving time of the peak of the data channel signal based on the peak receiving time of the random access channel signal; and despreading the data channel signal based on the peak receiving time of the data channel signal. The peak detecting step of the data channel signal may generate a spreading code for despreading the data channel signal based on the peak receiving time of the random access channel signal.
The method can be provided such that the peak detecting of the data channel signal may sequentially generate a plurality of spreading codes, each of which corresponds to the data channel signal of each of a plurality of symbol periods, based on the peak receiving time of the random access channel signal. The peak detecting of the data channel signal may: despread the data channel signal of the plurality of symbol periods using the plurality of spreading codes generated by the spreading code generating; store the despread data channel signals of the plurality of symbol periods; sum each of the stored data channel signals of the plurality of symbol periods; and detect the peak of the data channel signal from the summed data channel signal.
The spreading code generating step may start generating the spreading code when receiving the peak of the random access channel signal. The data channel signal storing step may start storing the despread data channel signal based on the peak receiving time of the random access channel signal.
This summary of the invention does not necessarily describe all necessary features so that the invention may also be a sub-combination of these described features.